Concentration of suspended solids



8 A. SCHEPMAN CONCENTRATION OF SUSPENDED SOLIDS Original Filed July 5.1961 June 29, 1965 3 Sheets-Sheet 1 INVENTOR. BERNE A.SCHEPMAN fiwwe wQTtTvMra June 29, 1965 B. A. SCHEPMAN CONCENTRATION OF SUSPENDED SOLIDSOriginal Filed July 5, 1961 3 Sheets-Sheet 2 v INV EN TOR.

BERNE A. SCHEPMAN "QM B. A. SCHEPMAN CONCENTRATION OF SUSPENDED SOLIDSJune 29, 1965 Original Filed July 3, 1961 3 Sheets-Sheet 5 INVENTOR.BERNE A. SCHEPMAN By i d QJ -k ommm United States Patent This is acontinuation of application Serial No. 121,478 filed July 3, 1961, andnow abandoned.

This invention relates generally to the concentration and recovery ofsolids from a suspending liquid; and in particular to the concentrationand recovery of extremely fine solids, such as kiln dust, leached finelyground ores,

and the like, which are normally resistant to concentration or difficultto concentrate by usual sedimentation methods and apparatus.

It is a primary object of the invention to provide ways and means foreifecting concentration and recovery of finely divided solids from asuspending liquid.

Another object is a provision of a specific apparatus for carrying outsuch concentration on a continuous basis.

A related object is the provision of an apparatus arrangement and amethod of operating the same for the wetting, leaching, concentrationand recovery of the dust discharged from a cement kiln.

In the art of sedimentation to effect separation of solids from asuspending liquid, it is Well known to concentrate such solids insedimentation apparatus by subjecting them to the stirring action ofpaddles or rakes in the bottom of the sedimentation basin. Normally,such stirring occurs for some vertical distance above the bottom of thebasin and is frequently effected by means of the members of the rakingarms to which blades are attached, vertically extending stilts or rodsto the bottom of which are appended rake blades for moving the settledmaterial to discharge, or stationary pickets extending above the arms.It has been demonstrated that such stirring action is necessary toobtain a sufiiciently high solids concentration in the dischargeunderfiow for subsequent process and handling requirements.

In such concentration of fine solids as heretofore practiced, a primaryproblem has been the continuous build up of solids on the supportingmechanism. Such build up places an undue burden on the equipment andrequires shut down for cleanup lest the load bearing capabilities of thestructure be exceeded. Moreover, the build up interferes with the normalstirring action.

Because solids accumulation is inevitable, usual prior practice has beento build massive mechanisms to sustain the load for an. economic periodof time before shut down. It has. long been known that less build upwill occur with a lighter structure presenting less surface, however,lighter structures are incapable of supporting any reasonable loads.

In the present invention, the foregoing problems are overcome by waysand means providing the required structure for raking along with thenecessary stirring and concentrating and having integrally therewithmeans for removing solids accumulation from the mechanism duringcontinuous operation. Significantly the invention enables the use ofrelatively light structures yet obviates the necessity for shut down toremove accumulated solids.

In accordance with the present invention, there is provided asedimentation basin or tank having a bottom and upstanding marginalsidewalls and a rotationally mounted raking mechanism of relativelylight structure having depending rake blades for moving settled materialacross the bottom of the basin to the discharge outlet. Above themechanism and rotating therewith is a plurality of undue build up ofalkali in the final clinker.

3,191,775 Patented June 29,- 1965 substantially vertical stirring rodsor pickets, constructed of fiexible spring steel or similar elasticmaterial; and means are provided in the tank for periodically contactingsuch pickets to deflect them from normal then suddenly release them fromthe deflectedposition. This deflection and sudden release imparts avibration to the pickets and to a lesser degree, to the entire structureto shake off solids accumulated thereon. At the same time, the stirringand kneading effects of the pickets, necessary to proper concentrationof solids, continues unimpeded.

As will be discussed in more detail hereinafter, a typical example offine solids requiring special concentrating techniques is to be found inthe cement industry where kiln dust must either be thoroughly wetted andconcentrated for recovery or be washed or leached then concentratedprior to return to the kiln in order to prevent Briefly, such systemsrecover kiln dust and subject it to a leaching operation to remove atleast a portion of contained alkali. The solids are concentrated inorder to return them to the kiln with an acceptably low moisturecontent. Heretofore, the cost of concentrating such leached solids hasbeen prohibitive primarily because of the difliculty of obtainingsufficiently high solids concentration in the sedimentation under-flow.As noted, higher convention, recovery and leaching of the cement kilndust for return to the system is renedered economicaly feasible.

In order that the invention and its practical application may be morereadily understood and carried into efiect, reference is made to theaccompanying drawings which show, for purposes of illustration, certainembodiments of the invention, the scope of which is defined by theappended claims rather than by any examples or preceding description.

In the drawings:

FIG. 1 is a simplified top elevational view of the concentrationapparatus embodying the invention.

FIG. 2 is a side sectional view of the apparatus of FIG. 1, certainparts being shown in elevation.

. FIGS. 3 and 3a are views showing, more or less diagrammatically, thefunction and operation of the selfcleaning concentrating mechanism. Inthe two figures .sirnilar reference numerals are used to designatesimilar elements. I

FIG. 4 is a perspective view of a cement dust leaching and recoverysystem embodying the invention. v The basic apparatus employed in theinvention comprises a tank 10 having a bottom 11 and upstandingsidewalls 12. There is provided a support beam 13, drive mechanism 14,rotatable center column 15 and laterally extending support arms 16afiixed to and rotatable with the center column 15.

Usual rake blades 17 are supplied for moving concentrated solids to acenter discharge 13 whence they are removed from the tank.

Feed is supplied via a suitable conduit 19 into a conventional feedwellor mechanism 21 to be distributed via radially extending tubes 22 intothe tank proper. As noted, settled material is removed via a suitabledischarge 18 while clarified liquor over flows as efiluent via adischarge launder 23. Floating scum is removed in usual fashion via ascum outlet 24 to which it is moved by scum skimmer 26. i i

Referring in particular to FIGS. 2 and 3, it will be noted that the rakesupporting arms 16 are provided with upstanding picket-like members 27which move through the slurry to eifect further dewatering andconcentration of the partially settled solids. As the rake arm 16rotates, the pickets 27 pass through the solids effecting stirring andconcentration, and eventually bear against a cross member 28 whichengages the picket members at a point above their bottom terminalconnection to the rake arm 16. Further rotation of the rake arms effectsdeflection of each picket member as it passes toward and past the crossmember. As the picket passes the cross member 28 it snaps rapidly backto its normal operating position. In the illustrated embodiment, thenormal position is shown as vertical, however, it may assume othernormal positions. Such deflection and release of the deflecting forceshakes the entire structure including the rake arm 16 and the subtendedblades to effect removal of accumulated solids. At the same time, thekneading and stirring action of the picket members continues withoutinterruption.

Although the deflector 28 is shown as closely adjacent the top of thepickets, it is within the scope of this invention to provide a scrapingaction by lowering the point of contact between the pickets anddeflectors.

In the system illustrated in FIG. 4 the invention is embodied in acement calcining and leaching operation. In such system, cement bearingmaterial is initially fed into a hopper 31 whence it is fed into thekiln 32 counter-currently to the hot gases. Dust discharged from thekiln passes through a dust collection system, generally designated 33,and the dust-free gases are discharged via a suitable conduit 34, blower36 and stack 37.

From the dust collector, fine dust is passed via a suitable conveyor 38to a further conveyor 39 whence it passes through a cyclone typecontactor 41 where it is wetted'with water for leaching thence passesinto a mixer 42 and finally into the feed conduit 19 for supply to theconcentration tank. Effluent is discharged at 30 to be conveyed by aconduit to discharge or further use, or via a branch line through aneutralizer 42 where the alkali content of the leach water may beneutralized by means of CO bearing gas from the stack 34. Neutralizedwater may be then discharged via a conduit 46. Use of the leach waterneutralizer is optional.

In the system illustrated, the fundamental goal is recovery of kilndust, however, the dust cannot be directly returned to kiln because itcontains an abnormally high percentage of alkali which would result inthe final kiln product having an excessive alkali content. In thiscnnection, it may be noted that the total alkali content (potassium andsodium alkali both reported as Na O) should not exceed 0.6% by weight inthe final product.

The reason for this is that alkali often reacts with certain aggregatesto cause chipping and flaking and these are standards set which must beobserved.

The usual raw material contains a significant amount of alkali a majorportion of which is discharged from the kiln with the dust. If the dustis wasted, the main clinker material will generally meet the ASTMspecifications of 0.6% alkali.- However, wasting kiln dust is extremelycostly and for that reason, leaching has been resorted to in order tolower its alkali content sufliciently to permit return to the kiln.

As noted, leaching requires a considerable amount of water andconsequently solids concentration is required in order to provide a dustof acceptably low moisture content for return to the kiln on an economicbasis.

Example A typical plant uses 1083. tons per day kiln feed containing0.6% total alkali (6.5 tons per day alkali). The required product is afinal clinker having less than 0.5% alkali. In order to accomplish thisyet maintain maximum production, kiln dust is collected and recycled.With the recycle load and the system in balance, 137 tons per day ofdust is added to the kilnofeed makinga total kiln feed of 1220 tons perday.

A large portion of the alkali is volatilized in the kiln and carried outin the dust. Thus, the kiln dust, which 4 amounts to tons per day,carries an alkali content of 4.41% (6.18 tons per day, alkali).Collected dust is Wetted with approximately 1260 tons per day of waterin the contactor, then concentrated for recycle to the kiln.

Utilizing the concentrator of the present invention in the above system,there is attained a 55% solids underflow containing 137 tons per dayleached solids having an insoluble alkali content of 1.84% and a solublealkali content of 29%, or a total of 2.85 tons per day alkali in therecycle dust. This, when combined with new feed material gives a kilnfeed with an alkali content of 0.77%. However, volatilization in thekiln accounts for a major portion of this alkali and the resultingclinker carries an average alkali content of 0.433% which is well belowthe acceptable figure in the area in which the operation is conducted.

In the same plant, utilizing the same raw material and rate of feed, butrecycling the dust without leaching, the kiln feed (including dust) was1.04% alkali and the ultimate clinker was 0.88% alkali whichiscompletely unacceptable. In this plant, it strict adherence to the0.6% maximum alkali content is observed, a large portion of the dust hasto be discarded unless there is an economic way to leach andconcentrate.

It is to be noted that the concentrator of the present invention is ableto operate continuously to yield an underflow containing 55% solids yetrequires no shut down for maintenance or clean up. If prior operation inthe same plant, but utilizing a sedimentation apparatus without the selfcleaning feature, the maximum period of operation was approximately 4weeks after which the entire system had to be closed down so that thesedimentation apparatus could be thoroughly cleaned of accumulatedsolids. It should be noted that cleaning of accumulated solids poses aserious problem because when the sedimentation unit is drained thebuoyancy effect of the liquid in the tank is lost and the full weight ofaccumulated solids bears on the mechanism. Thus, clean out must occur atrather frequent intervals lest the accumulation be so great that upondraining for clean-out the structure is loaded to failure.

From the foregoing it is seen that the present inven- .tion presents onthe one hand a system embodying a particular type of solidsconcentration in which there is effected concentration of the solids bya kneading action on a continuous basis under conditions whereby selfcleaning of the apparatus is made possibly thereby in turn makingpossible continuous operation of the entire dust collection and leachingsystem and rendering such system economically attractive.

The invention also provides a particular type apparatus and method ofoperating the same by which stirring of partially settled solids toeffect continuous dewatering to an acceptable consistency isaccomplished by means of upstanding substantially vertical flexiblepickets operating Within a zone of compression or compaction to effect akneading on the solids to force out additional water; such pickets beingcontinuously cleaned by deflection from normal position and release ofthe deflecting force.

It is also evident that the present invention makes full use of thenormally detrimental tendency for solids to deposit on the stirringmechanism by permitting such deposit concomitantly with the stirring,then release deposited solids to increase the density of the mass. Thisis a distinct advantage because deposited solids are of a much higherconcentration even than those in the concentrated mass, consequently,when released into the mass, contribute an increase in solidsconcentration. For purposes of this specification and claims, depositedsolids are referred to as substantially liquid-free because of their lowmoisture content compared to non-deposited solids.

It is also to be emphasized that the concept of the present invention,both as to method and apparatus, is not limited to the use in normalsedimentation apparatus but may be efliciently employed in any situationwhere it is necessary to subject a solids liquid mass to stirring andthere is danger of deposition of solids on the mechanism. Similarly, theinvention may be applied to any situation Where concentration of solidsby stirring is to be effected.

I claim:

1. Apparatus for sedimentation concentration of difficultly settleablesolids comprising a tank having a bottom and upstanding marginalsidewalls, means for supplying a solids-liquid suspension to said tank,a solids outlet in a lower portion of the tank for withdrawingconcentrated solids therefrom, efliuent overflow means in an upperportion of the tank, a rake support arm mounted for rotation in asubstantially horizontal plane in a lower portion of said tank andhaving a plurality of depending rake blades for moving settled solidstoward said solids outlet; and means for etfecting concentration ofsettled solids prior to discharge, comprising a plurality of elongatedflexible members mounted in spaced apart relationship on said rakesupport arm to extend generally upwardly therefrom, means for rotatablydriving said support, and deflecting means fixedly mounted in said tankin the path traced by said flexible members upon rotation of saidsupport to efifect periodic deflection and sudden release of saidflexible members.

2. Apparatus for sedimentation concentration of settleable solidscomprising a tank having a bottom and upstanding marginal sidewalls,means for supplying a solids-liquid suspension to said tank, a solidsoutlet in a lower portion of the tank for withdrawing concentratedsolids therefrom, eflluent overflow means in an upper portion of thetank, a rake support arm mounted for movement in a substantiallyhorizontal plane in a lower portion of said tank and having a pluralityof depending rake blades for moving settled solids toward said solidsoutlet; and means for effecting concentration of settled solids prior todischarge, comprising a plurality of elongated flexible members mountedin spaced-apart relationship on said rake support arm to extendgenerally upward- 1y therefrom, means for driving said support to moveit in said tank and deflecting means fixedly mounted in said tank in thepath traced by said flexible members upon movement of said support toeffect periodic deflection and sudden release of said flexible members.

3. Apparatus according to preceding claim 1 in which said deflectingmeans comprises an elongated member fixedly mounted transversely in saidtank at an elevation above said rake support arms.

4. Apparatus according to preceding claim 2 in which said deflectingmeans comprises an elongated member fixedly mounted transversely in saidtank at an elevation above said rake support arm.

5. Apparatus for sedimentation concentration of settleable solids,comprising a tank having a bottom and upstanding marginal sidewalls,means for supplying a solids-liquid suspension to said tank, means forwithdrawing settled solids from a lower portion of the tank, efiluentoutlet means in an upper portion of the tank, and means for etiectingconcentration of settled solids prior to discharge, comprising anelongated arm mounted for movement through said tank, a plurality ofspaced apart elongated flexible members secured at one end only to saidarm to extend generally transversely therefrom, means for driving saidarm to move it in said tank, and deflecting means fixedly mounted insaid tank in the path traced by the unsecured ends of said flexiblemembers upon movement of said arm to eflect periodic deflection andsudden release of said flexible members.

References Cited by the Examiner UNITED STATES PATENTS 2,881,922 4/59Kelly 2l0528 X 2,899,071 8/59 Bounin 210527 2,913,116 11/59 Cover 261-7X 2,793,866 3/61 Genter et al 210--519 REUBEN FRIEDMAN, PrimaryExaminer.

1. APPARATUS FOR SEDIMENTATION CONCENTRATION FO DIFFICULTLY SETTLEABLESOLIDS COMPRISING A TANK HAVING A BOTTOM AND UPSTANDING MARGINALSIDEWALLS, MEANS FOR SUPPLYING A SOLIDS-LIQUID SUSPENSION TO SAID TANK,A SOLIDS OUTLET IN A LOWER PORTION OF THE TANK FOR WITHDRAWINGCONCENTRATED SOLIDS THEREFROM, EFFLUENT OVERFLOW MEANS IN AN UPPERPORTION OF THE TANK, A RAKE SUPPORT ARM MOUNTED FOR ROTATION IN ASUBSTANTIALLY HORIZONTAL PLANE IN A LOWER PORTION OF SAID TANK ANDHAVING A PLURALITY OF DEPENDING RAKE BLADES FOR MOVING SETTLED SOLIDSTOWARD SAID SOLIDS OUTLET; AND MEANS FOR EFFECTING CONCENTRATION OFSETTLED SOLIDS PRIOR TO DISCHARGE, COMPRISING A PLURALITY OF ELONGATEDFLEXIBLE MEMBERS MOUNTED IN SPACED APART RELATIONSHIP ON SAID RAKESUPPORT ARM TO EXTEND GENERALLY UPWARDLY THEREFROM, MEANS FOR ROTATABLYDRIVING SAID SUPPORT, AND DEFLECTING MEANS FIXEDLY MOUNTED IN SAID TANKIN THE PATH TRACED BY SAID FLEXIBLE MEMBERS UPON ROTATION OF SAIDSUPPORT OF EFFECT PERIODIC DEFLECTION AND SUDDEN RELEASE OF SAIDFLEXIBLE MEMBERS.